man/systemd.special.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd.special">
   7
   8   <refentryinfo>
   9     <title>systemd.special</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd.special</refentrytitle>
  15     <manvolnum>7</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd.special</refname>
  20     <refpurpose>Special systemd units</refpurpose>
  21   </refnamediv>
  22
  23   <refsynopsisdiv><para>
  24     <!-- sort alphabetically, targets first --><filename>basic.target</filename>,
  25     <filename>bluetooth.target</filename>,
  26     <filename>cryptsetup-pre.target</filename>,
  27     <filename>cryptsetup.target</filename>,
  28     <filename>ctrl-alt-del.target</filename>,
  29     <filename>boot-complete.target</filename>,
  30     <filename>default.target</filename>,
  31     <filename>emergency.target</filename>,
  32     <filename>exit.target</filename>,
  33     <filename>final.target</filename>,
  34     <filename>getty.target</filename>,
  35     <filename>getty-pre.target</filename>,
  36     <filename>graphical.target</filename>,
  37     <filename>halt.target</filename>,
  38     <filename>hibernate.target</filename>,
  39     <filename>hybrid-sleep.target</filename>,
  40     <filename>suspend-then-hibernate.target</filename>,
  41     <filename>initrd-fs.target</filename>,
  42     <filename>initrd-root-device.target</filename>,
  43     <filename>initrd-root-fs.target</filename>,
  44     <filename>kbrequest.target</filename>,
  45     <filename>kexec.target</filename>,
  46     <filename>local-fs-pre.target</filename>,
  47     <filename>local-fs.target</filename>,
  48     <filename>machines.target</filename>
  49     <filename>multi-user.target</filename>,
  50     <filename>network-online.target</filename>,
  51     <filename>network-pre.target</filename>,
  52     <filename>network.target</filename>,
  53     <filename>nss-lookup.target</filename>,
  54     <filename>nss-user-lookup.target</filename>,
  55     <filename>paths.target</filename>,
  56     <filename>poweroff.target</filename>,
  57     <filename>printer.target</filename>,
  58     <filename>reboot.target</filename>,
  59     <filename>remote-cryptsetup.target</filename>,
  60     <filename>remote-fs-pre.target</filename>,
  61     <filename>remote-fs.target</filename>,
  62     <filename>rescue.target</filename>,
  63     <filename>rpcbind.target</filename>,
  64     <filename>runlevel2.target</filename>,
  65     <filename>runlevel3.target</filename>,
  66     <filename>runlevel4.target</filename>,
  67     <filename>runlevel5.target</filename>,
  68     <filename>shutdown.target</filename>,
  69     <filename>sigpwr.target</filename>,
  70     <filename>sleep.target</filename>,
  71     <filename>slices.target</filename>,
  72     <filename>smartcard.target</filename>,
  73     <filename>sockets.target</filename>,
  74     <filename>sound.target</filename>,
  75     <filename>suspend.target</filename>,
  76     <filename>swap.target</filename>,
  77     <filename>sysinit.target</filename>,
  78     <filename>system-update.target</filename>,
  79     <filename>system-update-pre.target</filename>,
  80     <filename>time-set.target</filename>,
  81     <filename>time-sync.target</filename>,
  82     <filename>timers.target</filename>,
  83     <filename>umount.target</filename>,
  84     <filename>usb-gadget.target</filename>,
  85     <!-- slices --><filename>-.slice</filename>,
  86     <filename>system.slice</filename>,
  87     <filename>user.slice</filename>,
  88     <filename>machine.slice</filename>,
  89     <!-- the rest --><filename>-.mount</filename>,
  90     <filename>dbus.service</filename>,
  91     <filename>dbus.socket</filename>,
  92     <filename>display-manager.service</filename>,
  93     <filename>init.scope</filename>,
  94     <filename>syslog.socket</filename>,
  95     <filename>system-update-cleanup.service</filename>
  96   </para></refsynopsisdiv>
  97
  98   <refsect1>
  99     <title>Description</title>
 100
 101     <para>A few units are treated specially by systemd. Many of them have
 102     special internal semantics and cannot be renamed, while others simply
 103     have a standard meaning and should be present on all systems.</para>
 104   </refsect1>
 105
 106   <refsect1>
 107     <title>Units managed by the system's service manager</title>
 108
 109     <refsect2>
 110       <title>Special System Units</title>
 111
 112       <variablelist>
 113         <varlistentry>
 114           <term><filename>-.mount</filename></term>
 115           <listitem>
 116             <para>The root mount point, i.e. the mount unit for the <filename>/</filename>
 117             path. This unit is unconditionally active, during the entire time the system is up, as
 118             this mount point is where the basic userspace is running from.</para>
 119           </listitem>
 120         </varlistentry>
 121
 122         <varlistentry>
 123           <term><filename>basic.target</filename></term>
 124           <listitem>
 125             <para>A special target unit covering basic boot-up.</para>
 126
 127             <para>systemd automatically adds dependency of the type
 128             <varname>After=</varname> for this target unit to all
 129             services (except for those with
 130             <varname>DefaultDependencies=no</varname>).</para>
 131
 132             <para>Usually, this should pull-in all local mount points plus
 133             <filename>/var</filename>, <filename>/tmp</filename> and
 134             <filename>/var/tmp</filename>, swap devices, sockets, timers,
 135             path units and other basic initialization necessary for general
 136             purpose daemons. The mentioned mount points are special cased
 137             to allow them to be remote.
 138             </para>
 139
 140             <para>This target usually does not pull in any non-target units
 141             directly, but rather does so indirectly via other early boot targets.
 142             It is instead meant as a synchronization point for late boot
 143             services. Refer to
 144             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 145             for details on the targets involved.
 146             </para>
 147           </listitem>
 148         </varlistentry>
 149         <varlistentry>
 150           <term><filename>boot-complete.target</filename></term>
 151           <listitem>
 152             <para>This target is intended as generic synchronization point for services that shall determine or act on
 153             whether the boot process completed successfully. Order units that are required to succeed for a boot process
 154             to be considered successful before this unit, and add a <varname>Requires=</varname> dependency from the
 155             target unit to them. Order units that shall only run when the boot process is considered successful after the
 156             target unit and pull in the target from it, also with <varname>Requires=</varname>. Note that by default this
 157             target unit is not part of the initial boot transaction, but is supposed to be pulled in only if required by
 158             units that want to run only on successful boots.</para>
 159
 160             <para>See
 161             <citerefentry><refentrytitle>systemd-boot-check-no-failures.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 162             for a service that implements a generic system health check and orders itself before
 163             <filename>boot-complete.target</filename>.</para>
 164
 165             <para>See
 166             <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 167             for a service that propagates boot success information to the boot loader, and orders itself after
 168             <filename>boot-complete.target</filename>.</para>
 169           </listitem>
 170         </varlistentry>
 171         <varlistentry>
 172           <term><filename>ctrl-alt-del.target</filename></term>
 173           <listitem>
 174             <para>systemd starts this target whenever Control+Alt+Del is
 175             pressed on the console. Usually, this should be aliased
 176             (symlinked) to <filename>reboot.target</filename>.</para>
 177           </listitem>
 178         </varlistentry>
 179         <varlistentry>
 180           <term><filename>cryptsetup.target</filename></term>
 181           <listitem>
 182             <para>A target that pulls in setup services for all
 183             encrypted block devices.</para>
 184           </listitem>
 185         </varlistentry>
 186         <varlistentry>
 187           <term><filename>dbus.service</filename></term>
 188           <listitem>
 189             <para>A special unit for the D-Bus bus daemon. As soon as
 190             this service is fully started up systemd will connect to it
 191             and register its service.</para>
 192           </listitem>
 193         </varlistentry>
 194         <varlistentry>
 195           <term><filename>dbus.socket</filename></term>
 196           <listitem>
 197             <para>A special unit for the D-Bus system bus socket. All
 198             units with <varname>Type=dbus</varname> automatically gain a
 199             dependency on this unit.</para>
 200           </listitem>
 201         </varlistentry>
 202         <varlistentry>
 203           <term><filename>default.target</filename></term>
 204           <listitem>
 205             <para>The default unit systemd starts at bootup. Usually,
 206             this should be aliased (symlinked) to
 207             <filename>multi-user.target</filename> or
 208             <filename>graphical.target</filename>.</para>
 209
 210             <para>The default unit systemd starts at bootup can be
 211             overridden with the <varname>systemd.unit=</varname> kernel
 212             command line option.</para>
 213           </listitem>
 214         </varlistentry>
 215         <varlistentry>
 216           <term><filename>display-manager.service</filename></term>
 217           <listitem>
 218             <para>The display manager service. Usually, this should be
 219             aliased (symlinked) to <filename>gdm.service</filename> or a
 220             similar display manager service.</para>
 221           </listitem>
 222         </varlistentry>
 223         <varlistentry>
 224           <term><filename>emergency.target</filename></term>
 225           <listitem>
 226             <para>A special target unit that starts an emergency shell on the main console. This
 227             target does not pull in any services or mounts. It is the most minimal version of
 228             starting the system in order to acquire an interactive shell; the only processes running
 229             are usually just the system manager (PID 1) and the shell process. This unit is supposed
 230             to be used with the kernel command line option <varname>systemd.unit=</varname>; it is
 231             also used when a file system check on a required file system fails, and boot-up cannot
 232             continue. Compare with <filename>rescue.target</filename>, which serves a similar
 233             purpose, but also starts the most basic services and mounts all file systems.</para>
 234
 235             <para>Use the <literal>systemd.unit=emergency.target</literal> kernel command line
 236             option to boot into this mode. A short alias for this kernel command line option is
 237             <literal>emergency</literal>, for compatibility with SysV.</para>
 238
 239             <para>In many ways booting into <filename>emergency.target</filename> is similar to the
 240             effect of booting with <literal>init=/bin/sh</literal> on the kernel command line,
 241             except that emergency mode provides you with the full system and service manager, and
 242             allows starting individual units in order to continue the boot process in steps.</para>
 243           </listitem>
 244         </varlistentry>
 245         <varlistentry>
 246           <term><filename>exit.target</filename></term>
 247           <listitem>
 248             <para>A special service unit for shutting down the system or
 249             user service manager. It is equivalent to
 250             <filename>poweroff.target</filename> on non-container
 251             systems, and also works in containers.</para>
 252
 253             <para>systemd will start this unit when it receives the
 254             <constant>SIGTERM</constant> or <constant>SIGINT</constant>
 255             signal when running as user service daemon.</para>
 256
 257             <para>Normally, this (indirectly) pulls in
 258             <filename>shutdown.target</filename>, which in turn should be
 259             conflicted by all units that want to be scheduled for
 260             shutdown when the service manager starts to exit.</para>
 261           </listitem>
 262         </varlistentry>
 263         <varlistentry>
 264           <term><filename>final.target</filename></term>
 265           <listitem>
 266             <para>A special target unit that is used during the shutdown
 267             logic and may be used to pull in late services after all
 268             normal services are already terminated and all mounts
 269             unmounted.
 270             </para>
 271           </listitem>
 272         </varlistentry>
 273         <varlistentry>
 274           <term><filename>getty.target</filename></term>
 275           <listitem>
 276             <para>A special target unit that pulls in statically
 277             configured local TTY <filename>getty</filename> instances.
 278             </para>
 279           </listitem>
 280         </varlistentry>
 281         <varlistentry>
 282           <term><filename>graphical.target</filename></term>
 283           <listitem>
 284             <para>A special target unit for setting up a graphical login
 285             screen. This pulls in
 286             <filename>multi-user.target</filename>.</para>
 287
 288             <para>Units that are needed for graphical logins shall add
 289             <varname>Wants=</varname> dependencies for their unit to
 290             this unit (or <filename>multi-user.target</filename>) during
 291             installation. This is best configured via
 292             <varname>WantedBy=graphical.target</varname> in the unit's
 293             <literal>[Install]</literal> section.</para>
 294           </listitem>
 295         </varlistentry>
 296         <varlistentry>
 297           <term><filename>hibernate.target</filename></term>
 298           <listitem>
 299             <para>A special target unit for hibernating the system. This
 300             pulls in <filename>sleep.target</filename>.</para>
 301           </listitem>
 302         </varlistentry>
 303         <varlistentry>
 304           <term><filename>hybrid-sleep.target</filename></term>
 305           <listitem>
 306             <para>A special target unit for hibernating and suspending
 307             the system at the same time. This pulls in
 308             <filename>sleep.target</filename>.</para>
 309           </listitem>
 310         </varlistentry>
 311         <varlistentry>
 312           <term><filename>suspend-then-hibernate.target</filename></term>
 313           <listitem>
 314             <para>A special target unit for suspending the system for a period
 315             of time, waking it and putting it into hibernate. This pulls in
 316             <filename>sleep.target</filename>.</para>
 317           </listitem>
 318         </varlistentry>
 319
 320         <varlistentry>
 321           <term><filename>halt.target</filename></term>
 322           <listitem>
 323             <para>A special target unit for shutting down and halting
 324             the system. Note that this target is distinct from
 325             <filename>poweroff.target</filename> in that it generally
 326             really just halts the system rather than powering it
 327             down.</para>
 328
 329             <para>Applications wanting to halt the system should not start this unit
 330             directly, but should instead execute <command>systemctl halt</command>
 331             (possibly with the <option>--no-block</option> option) or call
 332             <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 333             <command>org.freedesktop.systemd1.Manager.Halt</command> D-Bus method
 334             directly.</para>
 335           </listitem>
 336         </varlistentry>
 337         <varlistentry>
 338           <term><filename>init.scope</filename></term>
 339           <listitem>
 340             <para>This scope unit is where the system and service manager (PID 1) itself resides. It
 341             is active as long as the system is running.</para>
 342           </listitem>
 343         </varlistentry>
 344         <varlistentry>
 345           <term><filename>initrd-fs.target</filename></term>
 346           <listitem>
 347             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 348             automatically adds dependencies of type
 349             <varname>Before=</varname> to
 350             <filename>sysroot-usr.mount</filename> and all mount points
 351             found in <filename>/etc/fstab</filename> that have
 352             <option>x-initrd.mount</option> and not have
 353             <option>noauto</option> mount options set.</para>
 354           </listitem>
 355         </varlistentry>
 356         <varlistentry>
 357           <term><filename>initrd-root-device.target</filename></term>
 358           <listitem>
 359             <para>A special initrd target unit that is reached when the root filesystem device is available, but before
 360             it has been mounted.
 361             <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 362             and
 363             <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 364             automatically setup the appropriate dependencies to make this happen.
 365             </para>
 366           </listitem>
 367         </varlistentry>
 368         <varlistentry>
 369           <term><filename>initrd-root-fs.target</filename></term>
 370           <listitem>
 371             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 372             automatically adds dependencies of type
 373             <varname>Before=</varname> to the
 374             <filename>sysroot.mount</filename> unit, which is generated
 375             from the kernel command line.
 376             </para>
 377           </listitem>
 378         </varlistentry>
 379         <varlistentry>
 380           <term><filename>kbrequest.target</filename></term>
 381           <listitem>
 382             <para>systemd starts this target whenever Alt+ArrowUp is
 383             pressed on the console. Note that any user with physical access
 384             to the machine will be able to do this, without authentication,
 385             so this should be used carefully.</para>
 386           </listitem>
 387         </varlistentry>
 388         <varlistentry>
 389           <term><filename>kexec.target</filename></term>
 390           <listitem>
 391             <para>A special target unit for shutting down and rebooting
 392             the system via kexec.</para>
 393
 394             <para>Applications wanting to reboot the system should not start this unit
 395             directly, but should instead execute <command>systemctl kexec</command>
 396             (possibly with the <option>--no-block</option> option) or call
 397             <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 398             <command>org.freedesktop.systemd1.Manager.KExec</command> D-Bus method
 399             directly.</para>
 400           </listitem>
 401         </varlistentry>
 402         <varlistentry>
 403           <term><filename>local-fs.target</filename></term>
 404           <listitem>
 405             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 406             automatically adds dependencies of type
 407             <varname>Before=</varname> to all mount units that refer to
 408             local mount points for this target unit. In addition, it
 409             adds dependencies of type <varname>Wants=</varname> to this
 410             target unit for those mounts listed in
 411             <filename>/etc/fstab</filename> that have the
 412             <option>auto</option> mount option set.</para>
 413           </listitem>
 414         </varlistentry>
 415         <varlistentry>
 416           <term><filename>machines.target</filename></term>
 417           <listitem>
 418             <para>A standard target unit for starting all the containers
 419             and other virtual machines. See <filename>systemd-nspawn@.service</filename>
 420             for an example.</para>
 421           </listitem>
 422         </varlistentry>
 423         <varlistentry>
 424           <term><filename>multi-user.target</filename></term>
 425           <listitem>
 426             <para>A special target unit for setting up a multi-user
 427             system (non-graphical). This is pulled in by
 428             <filename>graphical.target</filename>.</para>
 429
 430             <para>Units that are needed for a multi-user system shall
 431             add <varname>Wants=</varname> dependencies for their unit to
 432             this unit during installation. This is best configured via
 433             <varname>WantedBy=multi-user.target</varname> in the unit's
 434             <literal>[Install]</literal> section.</para>
 435           </listitem>
 436         </varlistentry>
 437         <varlistentry>
 438           <term><filename>network-online.target</filename></term>
 439           <listitem>
 440             <para>Units that strictly require a configured network
 441             connection should pull in
 442             <filename>network-online.target</filename> (via a
 443             <varname>Wants=</varname> type dependency) and order
 444             themselves after it. This target unit is intended to pull in
 445             a service that delays further execution until the network is
 446             sufficiently set up. What precisely this requires is left to
 447             the implementation of the network managing service.</para>
 448
 449             <para>Note the distinction between this unit and
 450             <filename>network.target</filename>. This unit is an active
 451             unit (i.e. pulled in by the consumer rather than the
 452             provider of this functionality) and pulls in a service which
 453             possibly adds substantial delays to further execution. In
 454             contrast, <filename>network.target</filename> is a passive
 455             unit (i.e. pulled in by the provider of the functionality,
 456             rather than the consumer) that usually does not delay
 457             execution much. Usually, <filename>network.target</filename>
 458             is part of the boot of most systems, while
 459             <filename>network-online.target</filename> is not, except
 460             when at least one unit requires it. Also see <ulink
 461             url="https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 462             Services After the Network is up</ulink> for more
 463             information.</para>
 464
 465             <para>All mount units for remote network file systems
 466             automatically pull in this unit, and order themselves after
 467             it. Note that networking daemons that simply provide
 468             functionality to other hosts generally do not need to pull
 469             this in.</para>
 470
 471             <para>systemd automatically adds dependencies of type <varname>Wants=</varname> and
 472             <varname>After=</varname> for this target unit to all SysV init script service units
 473             with an LSB header referring to the <literal>$network</literal> facility.</para>
 474
 475             <para>Note that this unit is only useful during the original system start-up
 476             logic. After the system has completed booting up, it will not track the online state of
 477             the system anymore. Due to this it cannot be used as a network connection monitor
 478             concept, it is purely a one-time system start-up concept.</para>
 479             </listitem>
 480         </varlistentry>
 481         <varlistentry>
 482           <term><filename>paths.target</filename></term>
 483           <listitem>
 484             <para>A special target unit that sets up all path units (see
 485             <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 486             for details) that shall be active after boot.</para>
 487
 488             <para>It is recommended that path units installed by
 489             applications get pulled in via <varname>Wants=</varname>
 490             dependencies from this unit. This is best configured via a
 491             <varname>WantedBy=paths.target</varname> in the path unit's
 492             <literal>[Install]</literal> section.</para>
 493           </listitem>
 494         </varlistentry>
 495         <varlistentry>
 496           <term><filename>poweroff.target</filename></term>
 497           <listitem>
 498             <para>A special target unit for shutting down and powering
 499             off the system.</para>
 500
 501             <para>Applications wanting to power off the system should not start this unit
 502             directly, but should instead execute <command>systemctl poweroff</command>
 503             (possibly with the <option>--no-block</option> option) or call
 504             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 505             <command>org.freedesktop.login1.Manager.PowerOff</command> D-Bus method
 506             directly.</para>
 507
 508             <para><filename>runlevel0.target</filename> is an alias for
 509             this target unit, for compatibility with SysV.</para>
 510           </listitem>
 511         </varlistentry>
 512         <varlistentry>
 513           <term><filename>reboot.target</filename></term>
 514           <listitem>
 515             <para>A special target unit for shutting down and rebooting
 516             the system.</para>
 517
 518             <para>Applications wanting to reboot the system should not start this unit
 519             directly, but should instead execute <command>systemctl reboot</command>
 520             (possibly with the <option>--no-block</option> option) or call
 521             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 522             <command>org.freedesktop.login1.Manager.Reboot</command> D-Bus method
 523             directly.</para>
 524
 525             <para><filename>runlevel6.target</filename> is an alias for
 526             this target unit, for compatibility with SysV.</para>
 527           </listitem>
 528         </varlistentry>
 529         <varlistentry>
 530           <term><filename>remote-cryptsetup.target</filename></term>
 531           <listitem>
 532             <para>Similar to <filename>cryptsetup.target</filename>, but for encrypted
 533             devices which are accessed over the network. It is used for
 534             <citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 535             entries marked with <option>_netdev</option>.</para>
 536           </listitem>
 537         </varlistentry>
 538         <varlistentry>
 539           <term><filename>remote-fs.target</filename></term>
 540           <listitem>
 541             <para>Similar to <filename>local-fs.target</filename>, but
 542             for remote mount points.</para>
 543
 544             <para>systemd automatically adds dependencies of type
 545             <varname>After=</varname> for this target unit to all SysV
 546             init script service units with an LSB header referring to
 547             the <literal>$remote_fs</literal> facility.</para>
 548           </listitem>
 549         </varlistentry>
 550         <varlistentry>
 551           <term><filename>rescue.target</filename></term>
 552           <listitem>
 553             <para>A special target unit that pulls in the base system (including system mounts) and
 554             spawns a rescue shell. Isolate to this target in order to administer the system in
 555             single-user mode with all file systems mounted but with no services running, except for
 556             the most basic. Compare with <filename>emergency.target</filename>, which is much more
 557             reduced and does not provide the file systems or most basic services. Compare with
 558             <filename>multi-user.target</filename>, this target could be seen as
 559             <filename>single-user.target</filename>.</para>
 560
 561             <para><filename>runlevel1.target</filename> is an alias for this target unit, for
 562             compatibility with SysV.</para>
 563
 564             <para>Use the <literal>systemd.unit=rescue.target</literal> kernel command line option
 565             to boot into this mode. A short alias for this kernel command line option is
 566             <literal>1</literal>, for compatibility with SysV.</para>
 567           </listitem>
 568         </varlistentry>
 569         <varlistentry>
 570           <term><filename>runlevel2.target</filename></term>
 571           <term><filename>runlevel3.target</filename></term>
 572           <term><filename>runlevel4.target</filename></term>
 573           <term><filename>runlevel5.target</filename></term>
 574           <listitem>
 575             <para>These are targets that are called whenever the SysV
 576             compatibility code asks for runlevel 2, 3, 4, 5,
 577             respectively. It is a good idea to make this an alias for
 578             (i.e. symlink to) <filename>graphical.target</filename>
 579             (for runlevel 5) or <filename>multi-user.target</filename>
 580             (the others).</para>
 581           </listitem>
 582         </varlistentry>
 583         <varlistentry>
 584           <term><filename>shutdown.target</filename></term>
 585           <listitem>
 586             <para>A special target unit that terminates the services on
 587             system shutdown.</para>
 588
 589             <para>Services that shall be terminated on system shutdown
 590             shall add <varname>Conflicts=</varname> and
 591             <varname>Before=</varname> dependencies to this unit for
 592             their service unit, which is implicitly done when
 593             <varname>DefaultDependencies=yes</varname> is set (the
 594             default).</para>
 595           </listitem>
 596         </varlistentry>
 597         <varlistentry>
 598           <term><filename>sigpwr.target</filename></term>
 599           <listitem>
 600             <para>A special target that is started when systemd receives
 601             the SIGPWR process signal, which is normally sent by the
 602             kernel or UPS daemons when power fails.</para>
 603           </listitem>
 604         </varlistentry>
 605         <varlistentry>
 606           <term><filename>sleep.target</filename></term>
 607           <listitem>
 608             <para>A special target unit that is pulled in by
 609             <filename>suspend.target</filename>,
 610             <filename>hibernate.target</filename> and
 611             <filename>hybrid-sleep.target</filename> and may be used to
 612             hook units into the sleep state logic.</para>
 613           </listitem>
 614         </varlistentry>
 615         <varlistentry>
 616           <term><filename>slices.target</filename></term>
 617           <listitem>
 618             <para>A special target unit that sets up all slice units (see
 619             <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 620             for details) that shall always be active after boot. By default the generic
 621             <filename>system.slice</filename> slice unit as well as the root slice unit
 622             <filename>-.slice</filename> are pulled in and ordered before this unit (see
 623             below).</para>
 624
 625             <para>Adding slice units to <filename>slices.target</filename> is generally not
 626             necessary. Instead, when some unit that uses <varname>Slice=</varname> is started, the
 627             specified slice will be started automatically. Adding
 628             <varname>WantedBy=slices.target</varname> lines to the <literal>[Install]</literal>
 629             section should only be done for units that need to be always active. In that case care
 630             needs to be taken to avoid creating a loop through the automatic dependencies on
 631             "parent" slices.</para>
 632           </listitem>
 633         </varlistentry>
 634         <varlistentry>
 635           <term><filename>sockets.target</filename></term>
 636           <listitem>
 637             <para>A special target unit that sets up all socket
 638             units (see
 639             <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 640             for details) that shall be active after boot.</para>
 641
 642             <para>Services that can be socket-activated shall add
 643             <varname>Wants=</varname> dependencies to this unit for
 644             their socket unit during installation. This is best
 645             configured via a <varname>WantedBy=sockets.target</varname>
 646             in the socket unit's <literal>[Install]</literal>
 647             section.</para>
 648           </listitem>
 649         </varlistentry>
 650         <varlistentry>
 651           <term><filename>suspend.target</filename></term>
 652           <listitem>
 653             <para>A special target unit for suspending the system. This
 654             pulls in <filename>sleep.target</filename>.</para>
 655           </listitem>
 656         </varlistentry>
 657         <varlistentry>
 658           <term><filename>swap.target</filename></term>
 659           <listitem>
 660             <para>Similar to <filename>local-fs.target</filename>, but
 661             for swap partitions and swap files.</para>
 662           </listitem>
 663         </varlistentry>
 664         <varlistentry>
 665           <term><filename>sysinit.target</filename></term>
 666           <listitem>
 667             <para>systemd automatically adds dependencies of the types
 668             <varname>Requires=</varname> and <varname>After=</varname>
 669             for this target unit to all services (except for those with
 670             <varname>DefaultDependencies=no</varname>).</para>
 671
 672             <para>This target pulls in the services required for system
 673             initialization. System services pulled in by this target should
 674             declare <varname>DefaultDependencies=no</varname> and specify
 675             all their dependencies manually, including access to anything
 676             more than a read only root filesystem. For details on the
 677             dependencies of this target, refer to
 678             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 679             </para>
 680           </listitem>
 681         </varlistentry>
 682         <varlistentry>
 683           <term><filename>syslog.socket</filename></term>
 684           <listitem>
 685             <para>The socket unit syslog implementations should listen
 686             on. All userspace log messages will be made available on
 687             this socket. For more information about syslog integration,
 688             please consult the <ulink
 689             url="https://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 690             Interface</ulink> document.</para>
 691           </listitem>
 692         </varlistentry>
 693         <varlistentry>
 694           <term><filename>system-update.target</filename></term>
 695           <term><filename>system-update-pre.target</filename></term>
 696           <term><filename>system-update-cleanup.service</filename></term>
 697           <listitem>
 698             <para>A special target unit that is used for offline system updates.
 699             <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 700             will redirect the boot process to this target if <filename>/system-update</filename>
 701             exists. For more information see
 702             <citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 703             </para>
 704
 705             <para>Updates should happen before the <filename>system-update.target</filename> is
 706             reached, and the services which implement them should cause the machine to reboot. The
 707             main units executing the update should order themselves after
 708             <filename>system-update-pre.target</filename> but not pull it in. Services which want to
 709             run during system updates only, but before the actual system update is executed should
 710             order themselves before this unit and pull it in. As a safety measure, if this does not
 711             happen, and <filename>/system-update</filename> still exists after
 712             <filename>system-update.target</filename> is reached,
 713             <filename>system-update-cleanup.service</filename> will remove this symlink and reboot
 714             the machine.</para>
 715           </listitem>
 716         </varlistentry>
 717         <varlistentry>
 718           <term><filename>timers.target</filename></term>
 719           <listitem>
 720             <para>A special target unit that sets up all timer units
 721             (see
 722             <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 723             for details) that shall be active after boot.</para>
 724
 725             <para>It is recommended that timer units installed by
 726             applications get pulled in via <varname>Wants=</varname>
 727             dependencies from this unit. This is best configured via
 728             <varname>WantedBy=timers.target</varname> in the timer
 729             unit's <literal>[Install]</literal> section.</para>
 730           </listitem>
 731         </varlistentry>
 732         <varlistentry>
 733           <term><filename>umount.target</filename></term>
 734           <listitem>
 735             <para>A special target unit that unmounts all mount and
 736             automount points on system shutdown.</para>
 737
 738             <para>Mounts that shall be unmounted on system shutdown
 739             shall add Conflicts dependencies to this unit for their
 740             mount unit, which is implicitly done when
 741             <varname>DefaultDependencies=yes</varname> is set (the
 742             default).</para>
 743           </listitem>
 744         </varlistentry>
 745
 746       </variablelist>
 747     </refsect2>
 748
 749     <refsect2>
 750       <title>Special System Units for Devices</title>
 751
 752       <para>Some target units are automatically pulled in as devices of
 753       certain kinds show up in the system. These may be used to
 754       automatically activate various services based on the specific type
 755       of the available hardware.</para>
 756
 757       <variablelist>
 758         <varlistentry>
 759           <term><filename>bluetooth.target</filename></term>
 760           <listitem>
 761             <para>This target is started automatically as soon as a
 762             Bluetooth controller is plugged in or becomes available at
 763             boot.</para>
 764
 765             <para>This may be used to pull in Bluetooth management
 766             daemons dynamically when Bluetooth hardware is found.</para>
 767           </listitem>
 768         </varlistentry>
 769         <varlistentry>
 770           <term><filename>printer.target</filename></term>
 771           <listitem>
 772             <para>This target is started automatically as soon as a
 773             printer is plugged in or becomes available at boot.</para>
 774
 775             <para>This may be used to pull in printer management daemons
 776             dynamically when printer hardware is found.</para>
 777           </listitem>
 778         </varlistentry>
 779         <varlistentry>
 780           <term><filename>smartcard.target</filename></term>
 781           <listitem>
 782             <para>This target is started automatically as soon as a
 783             smartcard controller is plugged in or becomes available at
 784             boot.</para>
 785
 786             <para>This may be used to pull in smartcard management
 787             daemons dynamically when smartcard hardware is found.</para>
 788           </listitem>
 789         </varlistentry>
 790         <varlistentry>
 791           <term><filename>sound.target</filename></term>
 792           <listitem>
 793             <para>This target is started automatically as soon as a
 794             sound card is plugged in or becomes available at
 795             boot.</para>
 796
 797             <para>This may be used to pull in audio management daemons
 798             dynamically when audio hardware is found.</para>
 799           </listitem>
 800         </varlistentry>
 801         <varlistentry>
 802           <term><filename>usb-gadget.target</filename></term>
 803           <listitem>
 804             <para>This target is started automatically as soon as a
 805             USB Device Controller becomes available at boot.</para>
 806
 807             <para>This may be used to pull in usb gadget
 808             dynamically when UDC hardware is found.</para>
 809           </listitem>
 810         </varlistentry>
 811       </variablelist>
 812     </refsect2>
 813
 814     <refsect2>
 815       <title>Special Passive System Units </title>
 816
 817       <para>A number of special system targets are defined that can be
 818       used to properly order boot-up of optional services. These targets
 819       are generally not part of the initial boot transaction, unless
 820       they are explicitly pulled in by one of the implementing services.
 821       Note specifically that these <emphasis>passive</emphasis> target
 822       units are generally not pulled in by the consumer of a service,
 823       but by the provider of the service. This means: a consuming
 824       service should order itself after these targets (as appropriate),
 825       but not pull it in. A providing service should order itself before
 826       these targets (as appropriate) and pull it in (via a
 827       <varname>Wants=</varname> type dependency).</para>
 828
 829       <para>Note that these passive units cannot be started manually,
 830       i.e. <literal>systemctl start time-sync.target</literal> will fail
 831       with an error. They can only be pulled in by dependency. This is
 832       enforced since they exist for ordering purposes only and thus are
 833       not useful as only unit within a transaction.</para>
 834
 835       <variablelist>
 836         <varlistentry>
 837           <term><filename>cryptsetup-pre.target</filename></term>
 838           <listitem>
 839             <para>This passive target unit may be pulled in by services
 840             that want to run before any encrypted block device is set
 841             up. All encrypted block devices are set up after this target
 842             has been reached. Since the shutdown order is implicitly the
 843             reverse start-up order between units, this target is
 844             particularly useful to ensure that a service is shut down
 845             only after all encrypted block devices are fully
 846             stopped.</para>
 847           </listitem>
 848         </varlistentry>
 849         <varlistentry>
 850           <term><filename>getty-pre.target</filename></term>
 851           <listitem>
 852             <para>A special passive target unit. Users of this target
 853             are expected to pull it in the boot transaction via
 854             a dependency (e.g. <varname>Wants=</varname>). Order your
 855             unit before this unit if you want to make use of the console
 856             just before <filename>getty</filename> is started.
 857             </para>
 858           </listitem>
 859         </varlistentry>
 860         <varlistentry>
 861           <term><filename>local-fs-pre.target</filename></term>
 862           <listitem>
 863             <para>This target unit is
 864             automatically ordered before
 865             all local mount points marked
 866             with <option>auto</option>
 867             (see above). It can be used to
 868             execute certain units before
 869             all local mounts.</para>
 870           </listitem>
 871         </varlistentry>
 872         <varlistentry>
 873           <term><filename>network.target</filename></term>
 874           <listitem>
 875             <para>This unit is supposed to indicate when network
 876             functionality is available, but it is only very weakly
 877             defined what that is supposed to mean, with one exception:
 878             at shutdown, a unit that is ordered after
 879             <filename>network.target</filename> will be stopped before
 880             the network — to whatever level it might be set up then —
 881             is shut down. It is hence useful when writing service files
 882             that require network access on shutdown, which should order
 883             themselves after this target, but not pull it in. Also see
 884             <ulink url="https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 885             Services After the Network is up</ulink> for more
 886             information. Also see
 887             <filename>network-online.target</filename> described
 888             above.</para>
 889           </listitem>
 890         </varlistentry>
 891         <varlistentry>
 892           <term><filename>network-pre.target</filename></term>
 893           <listitem>
 894             <para>This passive target unit may be pulled in by services
 895             that want to run before any network is set up, for example
 896             for the purpose of setting up a firewall. All network
 897             management software orders itself after this target, but
 898             does not pull it in.</para>
 899           </listitem>
 900         </varlistentry>
 901         <varlistentry>
 902           <term><filename>nss-lookup.target</filename></term>
 903           <listitem>
 904             <para>A target that should be used as synchronization point for all host/network name
 905             service lookups. Note that this is independent of UNIX user/group name lookups for which
 906             <filename>nss-user-lookup.target</filename> should be used.  All services for which the
 907             availability of full host/network name resolution is essential should be ordered after
 908             this target, but not pull it in. systemd automatically adds dependencies of type
 909             <varname>After=</varname> for this target unit to all SysV init script service units
 910             with an LSB header referring to the <literal>$named</literal> facility.</para>
 911           </listitem>
 912         </varlistentry>
 913         <varlistentry>
 914           <term><filename>nss-user-lookup.target</filename></term>
 915           <listitem>
 916             <para>A target that should be used as synchronization point for all regular UNIX
 917             user/group name service lookups. Note that this is independent of host/network name
 918             lookups for which <filename>nss-lookup.target</filename> should be used. All services
 919             for which the availability of the full user/group database is essential should be
 920             ordered after this target, but not pull it in. All services which provide parts of the
 921             user/group database should be ordered before this target, and pull it in. Note that this
 922             unit is only relevant for regular users and groups — system users and groups are
 923             required to be resolvable during earliest boot already, and hence do not need any
 924             special ordering against this target.</para>
 925           </listitem>
 926         </varlistentry>
 927         <varlistentry>
 928           <term><filename>remote-fs-pre.target</filename></term>
 929           <listitem>
 930             <para>This target unit is automatically ordered before all
 931             mount point units (see above) and cryptsetup devices
 932             marked with the <option>_netdev</option>. It can be used to run
 933             certain units before remote encrypted devices and mounts are established.
 934             Note that this unit is generally not part of the initial
 935             transaction, unless the unit that wants to be ordered before
 936             all remote mounts pulls it in via a
 937             <varname>Wants=</varname> type dependency. If the unit wants
 938             to be pulled in by the first remote mount showing up, it
 939             should use <filename>network-online.target</filename> (see
 940             above).</para>
 941           </listitem>
 942         </varlistentry>
 943         <varlistentry>
 944           <term><filename>rpcbind.target</filename></term>
 945           <listitem>
 946             <para>The portmapper/rpcbind pulls in this target and orders
 947             itself before it, to indicate its availability. systemd
 948             automatically adds dependencies of type
 949             <varname>After=</varname> for this target unit to all SysV
 950             init script service units with an LSB header referring to
 951             the <literal>$portmap</literal> facility.</para>
 952           </listitem>
 953         </varlistentry>
 954         <varlistentry>
 955           <term><filename>time-set.target</filename></term>
 956           <listitem>
 957             <para>Services responsible for setting the system clock from
 958             a local source (such as a maintained timestamp file or
 959             imprecise real-time clock) should pull in this target and
 960             order themselves before it.  Services where approximate time
 961             is desired should be ordered after this unit, but not pull
 962             it in.  This target does not provide the accuracy guarantees
 963             of <filename>time-sync.target</filename>.</para>
 964           </listitem>
 965         </varlistentry>
 966         <varlistentry>
 967           <term><filename>time-sync.target</filename></term>
 968           <listitem>
 969             <para>Services responsible for synchronizing the system
 970             clock from a remote source (such as NTP client
 971             implementations) should pull in this target and order
 972             themselves before it. All services where correct time is
 973             essential should be ordered after this unit, but not pull it
 974             in. systemd automatically adds dependencies of type
 975             <varname>After=</varname> for this target unit to all SysV
 976             init script service units with an LSB header referring to
 977             the <literal>$time</literal> facility. </para>
 978           </listitem>
 979         </varlistentry>
 980       </variablelist>
 981     </refsect2>
 982
 983     <refsect2>
 984       <title>Special Slice Units</title>
 985
 986       <para>There are four <literal>.slice</literal> units which form the basis of the hierarchy for
 987       assignment of resources for services, users, and virtual machines or containers. See
 988       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 989       for details about slice units.</para>
 990
 991       <variablelist>
 992         <varlistentry>
 993           <term><filename>-.slice</filename></term>
 994           <listitem>
 995             <para>The root slice is the root of the slice hierarchy. It usually does not contain
 996             units directly, but may be used to set defaults for the whole tree.</para>
 997           </listitem>
 998         </varlistentry>
 999
1000         <varlistentry>
1001           <term><filename>system.slice</filename></term>
1002           <listitem>
1003             <para>By default, all system services started by
1004             <command>systemd</command> are found in this slice.</para>
1005           </listitem>
1006         </varlistentry>
1007
1008         <varlistentry>
1009           <term><filename>user.slice</filename></term>
1010           <listitem>
1011             <para>By default, all user processes and services started on
1012             behalf of the user, including the per-user systemd instance
1013             are found in this slice.  This is pulled in by
1014             <filename>systemd-logind.service</filename></para>
1015           </listitem>
1016         </varlistentry>
1017
1018         <varlistentry>
1019           <term><filename>machine.slice</filename></term>
1020           <listitem>
1021             <para>By default, all virtual machines and containers
1022             registered with <command>systemd-machined</command> are
1023             found in this slice.  This is pulled in by
1024             <filename>systemd-machined.service</filename></para>
1025           </listitem>
1026         </varlistentry>
1027       </variablelist>
1028     </refsect2>
1029   </refsect1>
1030
1031   <refsect1>
1032     <title>Units managed by the user's service manager</title>
1033
1034     <refsect2>
1035       <title>Special User Units</title>
1036
1037       <para>When systemd runs as a user instance, the following special
1038       units are available:</para>
1039
1040       <variablelist>
1041         <varlistentry>
1042           <term><filename>default.target</filename></term>
1043           <listitem>
1044             <para>This is the main target of the user session, started by default. Various services that
1045             compose the normal user session should be pulled into this target. In this regard,
1046             <filename>default.target</filename> is similar to <filename>multi-user.target</filename> in the
1047             system instance, but it is a real unit, not an alias.</para>
1048           </listitem>
1049         </varlistentry>
1050       </variablelist>
1051
1052       <para>In addition, the following units are available which have definitions similar to their
1053       system counterparts:
1054       <filename>exit.target</filename>,
1055       <filename>shutdown.target</filename>,
1056       <filename>sockets.target</filename>,
1057       <filename>timers.target</filename>,
1058       <filename>paths.target</filename>,
1059       <filename>bluetooth.target</filename>,
1060       <filename>printer.target</filename>,
1061       <filename>smartcard.target</filename>,
1062       <filename>sound.target</filename>.</para>
1063     </refsect2>
1064
1065     <refsect2>
1066       <title>Special Passive User Units</title>
1067
1068       <variablelist>
1069         <varlistentry>
1070           <term><filename>graphical-session.target</filename></term>
1071           <listitem>
1072             <para>This target is active whenever any graphical session is running. It is used to
1073             stop user services which only apply to a graphical (X, Wayland, etc.) session when the
1074             session is terminated. Such services should have
1075             <literal>PartOf=graphical-session.target</literal> in their <literal>[Unit]</literal>
1076             section. A target for a particular session (e. g.
1077             <filename>gnome-session.target</filename>) starts and stops
1078             <literal>graphical-session.target</literal> with
1079             <literal>BindsTo=graphical-session.target</literal>.</para>
1080
1081             <para>Which services are started by a session target is determined by the
1082             <literal>Wants=</literal> and <literal>Requires=</literal> dependencies.  For services
1083             that can be enabled independently, symlinks in <literal>.wants/</literal> and
1084             <literal>.requires/</literal> should be used, see
1085             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1086             Those symlinks should either be shipped in packages, or should be added dynamically
1087             after installation, for example using <literal>systemctl add-wants</literal>, see
1088             <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
1089             </para>
1090
1091             <example>
1092               <title>Nautilus as part of a GNOME session</title>
1093
1094               <para><literal>gnome-session.target</literal> pulls in Nautilus as top-level service:</para>
1095
1096               <programlisting>[Unit]
1097   Description=User systemd services for GNOME graphical session
1098   Wants=nautilus.service
1099   BindsTo=graphical-session.target</programlisting>
1100
1101               <para><literal>nautilus.service</literal> gets stopped when the session stops:</para>
1102
1103               <programlisting>[Unit]
1104   Description=Render the desktop icons with Nautilus
1105   PartOf=graphical-session.target
1106
1107   [Service]
1108   …</programlisting>
1109             </example>
1110           </listitem>
1111         </varlistentry>
1112
1113         <varlistentry>
1114           <term><filename>graphical-session-pre.target</filename></term>
1115           <listitem>
1116             <para>This target contains services which set up the environment or global configuration
1117             of a graphical session, such as SSH/GPG agents (which need to export an environment
1118             variable into all desktop processes) or migration of obsolete d-conf keys after an OS
1119             upgrade (which needs to happen before starting any process that might use them). This
1120             target must be started before starting a graphical session like
1121             <filename>gnome-session.target</filename>.</para>
1122           </listitem>
1123         </varlistentry>
1124       </variablelist>
1125     </refsect2>
1126   </refsect1>
1127
1128   <refsect1>
1129       <title>See Also</title>
1130       <para>
1131         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1132         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1133         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1134         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1135         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1136         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1137         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1138         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1139         <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1140       </para>
1141   </refsect1>
1142
1143 </refentry>